Leatherjackets are the larvae grubs of the Crane Fly (Daddy Longlegs.) Leatherjackets in lawns are a real pest and can have severe consequences unless killed. They are a pest of the lawn, for they eat the roots of the grass plants causing the grass to die.
They can also be a considerable pest in other parts of the garden - but not so noticeable - unless you have vegetable root crops - for roots of plants are their source of food until they emerge from under the ground and turn into Craneflies.
Leatherjackets in the Lawn
A small infestation is nothing to worry about, however if you have a lawn full of leatherjackets then the effect can be quite dramatic. In worse cases, resulting in much of the lawn dying and needing substantial remedial treatment.
First signs of leatherjacket Pests attacking your lawn are during the spring and summer, when small yellowing patches start to appear in the lawn. These eventually turn into brown patches in the grass. This is the result of the grubs feeding upon the roots of the grass. The severity of the problem is dependent upon the number of leatherjackets, and can start as just a few small patches a few inches across hardly noticeable in an average lawn, but a considerable lawn pest if not treated - killed.
Other signs of leatherjackets in lawns will be birds pecking at the lawn to get at the grubs mainly starlings, though members of the crow family are also partial to a feast of leather jackets - crows and magpies in particular. The birds also do a good job of aerating the lawn, for their beaks can penetrate several inches. It does no damage to the lawn.
You can do an easy follow-up analysis to see the cause, by simply lifting an area of grass where the problem exists. If it is leatherjackets in your lawn, they will be seen no more than a few inches below the turf/soil surface.
If you do not treat the leatherjacket pests, you will also see a large number of Crane flies hovering about the lawn area as the grubs emerge as Daddy Longlegs Flies.
These Adult flies then lay eggs in the lawn during autumn, which shortly hatch and start feeding on the lawn roots. The feeding normally stops in winter unless it is mild but soon resume again in the spring thereby completing the cycle as above for leatherjackets in lawns.
The picture shows the damage caused by leatherjacket pests. The browning of the lawn is caused by the leatherjacket larvae/grubs, eating the lawn grass roots just below the surface. You should also be able to see a few peck holes in the top right corner.
